In many technical applications, use is made of heat shields which have to stand up to hot gases at between 1000 and 1600 degrees Celsius. In particular gas turbines, such as are used in electricity-generating power plants and in aircraft engines, have accordingly large surfaces within the combustion chambers, which surfaces are to be protected by heat shields. Because of thermal expansion and because of large dimensions, the heat shield must be comprised of a multiplicity of individual, in general ceramic, heat shield tiles which are attached to a supporting structure on which they are spaced apart from one another with a sufficient gap. This gap between tiles provides the heat shield elements with sufficient space for thermal expansion. However, as the gap also makes it possible for the hot combustion gases to make direct contact with the metallic supporting structure and the holding elements, cooling air is injected, as a countermeasure, through the gaps in the direction of the combustion chamber.
A generic heat shield thus comprises a supporting structure and a number of heat shield tiles which are releasably attached to the supporting structure by means of tile holders, wherein each heat shield tile has a cold side oriented towards the supporting structure and a hot side which is opposite the cold side and which can be exposed to a hot medium. Each of the tile holders has at least one holding section for attaching to a heat shield tile and an attachment section which can be attached to the supporting structure. For the purpose of protection from hot gases, at least one cooling air passage is provided in the supporting structure.
For the purpose of attaching the tile holders to the supporting structure, circular circumferential and parallel attachment slots can be provided in the supporting structure. In this case, the tile holders are pushed one after the other with their attachment sections into the attachment slots, wherein subsequent tile holders block the position of the previously positioned tile holders. It is thus possible for a circular circumferential row of heat shield tiles to be attached to the supporting structure within a combustion chamber of a gas turbine.
EP 1 701 095 A1 discloses a heat shield of a combustion chamber of a gas turbine with a supporting structure and a number of heat shield tiles releasably arranged on the supporting structure. For the purpose of protecting the combustion chamber wall, the heat shield tiles are arranged on the supporting structure so as to cover a large area while leaving expansion gaps. Each heat shield tile has a cold side oriented towards the supporting structure and a hot side which is opposite the cold side and which can be exposed to a hot medium. The heat shield tiles are each resiliently attached to the supporting structure by means of four metallic tile holders. To that end, each tile holder comprises a holding section in the form of a gripping section and an attachment section. In every heat shield tile side, holding slots are introduced on two opposite circumferential sides, such that the gripping sections of the tile holders can engage in the opposite side holding slots in order to hold the heat shield tile. The tile holders facing the heat shield tile and attached in this manner are guided in the supporting structure with their attachment section in an attachment slot running beneath the heat shield tile. To provide protection from hot gases, the gripping sections of the metallic tile holders are cooled. To that end, openings are introduced into the tile holders in the region of the holding section and into the holding bars of the heat shield tiles, which openings are flush with a cooling air bore arranged in the supporting structure, such that cooling air flowing in a direct line from the cooling air bore impinges on a cold side of the gripping section.
In spite of this cooling of the gripping sections according to the prior art, it is possible when the heat shield is exposed to hot gas for hot gas to penetrate into the region of the expansion gaps between the heat shield tiles. The hot gas can then propagate beneath the heat shield and can cause scaling on the supporting structure.